Hydrostatic transmissions and the like are normally selectively placed in a forward or reverse mode of operation upon actuation of a rotary control shaft. A conventional actuating mechanism therefor is oftentimes unduly complex and requires close manufacturing tolerances to precisely control actuation of the transmission. In addition, many such mechanisms include linkage systems which exhibit excessive input torque characteristics.
One approach to alleviating the latter problem is to reduce the preload on an override spring link and by further reducing related friction in the linkage system. However, such preload cannot be reduced without also reducing the preload on the centering spring employed in the servovalve controlling operation of the transmission which is relatively low in magnitude to start with. Attempts to increase the mechanical advantage of the treadle of such linkage system have proved impractical since treadle motion would necessarily require a substantial increase. Also, the design of present day engine governor systems render it impractical to reduce input forces applied thereto.